Cyanogen compounds



INVENTOR Parma/vo H. HQQTIGHN.

1' SATTORNEY WITNESSES:

.peratures below its boiling point. `gen bromide, as well as the metalhalide cata- Patented Feb. 13, 1951 UNITED STATES PATENT OFFICE CYANOGEN COMPOUNDS Raymond H. Hartigan, Rensselaer, N. Y., assigner toKoppers Company. Inc., Pittsburgh, Pa., -a

corporation of Delaware Application December 29, 1945, Serial No.638,399

`1 This invention vrelates to the production of cyanuric halides. Moreparticularly the invention relates to the production of cyanuric halide'from cyanogen bromide.

Melamine resins may be made by the amination of cyanuric chloride.Cyanuric chloride may be -made by the `polymerization of cyanogenchloride. Cyanogen Achloride has a melting point of 16 C., a Yboiling`point of 13.8 C., and is a gas at normal temperature and pressure. gasis quite toxic so that the chlorination process is carried out withdiiiiculty in special equipment and at a comparatively high cost.

Cyanogen bromide has a melting :point of 52 C. and a boiling point of61.6 C. `So that it may be handled as a solid. I have found that`cyanogen bromide may be eiciently polymerized with a metallic halidecatalyst by treatment `at tem- The cyanois extracted 'from coalcarbonizati'on gas, 'suchas coke oven, and coal gas. I have found thatcyanogen bromide may be made by the ydirect bromination of HCN, NaCN orCa(CN)z accord- 'ing to the lformulae NaCN+Br2=BrCN+NeSBrHCN-i-Brz-:BI'CN-l-HBI' CaiCN) 2-i-2Br2=2CNBr-Cal3r2 If a molarequivalent of hydrocyanic acid is very strong hydrobromic acid solutionis formed which acts to hydrolyze the cyanogen bromide to form ammoniumbromide NHiBr and CO2.

This reaction takes place with explosive violence when the concentrationof HBr is high. yIt is important, therefore, that the bromination oihydrocyanic acid should be carried out so as to avoid explosivereactions and a loss of c yanogen `'constituent's.

The

I9 Claims. (Cl. 26o-248) kio 'directly brominated with elementalbromine, a

When the 'synthesis is carried out between the alkali and alkaline earthmetal cyanides with 'aqueous bromine in the presence of sulphuric acid,ammonium bromide is formed as a hydrolysis product, particularly ifstrong sulphuric acid is used.

The primary object of the present invention is to provide a process foreiiciently .producing cyanuric halides.

Another object of the invention vis to provide a process of producingcyanogen bromide by 4the direct bromination of hydrocyanic acid or Tametal cyanide With elemental bromine.

A 'further object of 'the invention 'is to provide a process oiproducing mixed cyanuric halides.`

With these and other objects in View the Vinl vention consists in theprocess of producing cyanuric halides hereinafter described andparticularly defined in the claims. y

Hydrocyanic acid I-ICN may be recovered from coke oven gas by scrubbingthe mixture of gaseous HCN, CO2 and HzS resulting from. the .hot vacuumactication process with hot water. In this process as an average a 4%aqueous hydro.- cyanio acid solution substantially free of HzS and CO2may be recovered. The alkali metal cyanides are made in comparativelylarge quantities and at present are the `main raw .material from whichcyanogen halides are made..

I have found that the `I-ICN may be! directly brominated to formcyanogen bromide by the treatment with elemental Vbromine, This processmay be carried out in an apparatus illus-- trated in the accompanyingdrawing which is 'a diagrammatic ilow sheet ci an 'apparatus forproducing cyanuric halide from hydrocyanic acid. v

Referring to the drawing., the hydrocyanic acid is placed in a jacketedcontainer l0 Vand passes through a dropping stein I2 into a body ofbromine and water in a .iaclreted mixer I4. The hydrocyanic acid isslowly added to the bromine `Water mixture with constant stirring,'while 'the contents are maintained at .a temperature below 23 C. toavoid loss of reactants by volatilizatlon and to obtain an eiiicientprecipitation of cyano-gen bromide. 'When the hydrogen cyanide `has beenadmitted the reaction mixture consists of a colorless hydrobromic acidsolution lcontaining an abundance of White, crystalline cyanogen bromidein suspension. The cooling solution is withdrawn from the jacket of themixer M and thereafter steam is introduced for heating the---nitroparaflins.

bromide and hydrobromic acid. Thereupon the cyanogen bromide isdistilled out of the mixture and passes through a line I6 into atemperature controlled tube I8, then into a cooled jacketed chamber 20,where the cyanogen bromide solidies.

The cyanogen bromide preferably is polymerl ized togproduce l.agcyanurichalide by a catalytic polymerization in contact with a metal halide,such as an aluminum chloride or aluminum bromide. Metal halide catalystsare preferably in an anhydrous state and as such may be readily dis- .4l centration of HCN. The percentage equivalent of HCN charged to theconverter may be represented I by the formula:

solved in a nitroparaflin hydrocarbon solvent such as nitromethane,nitroethane, nitropropane or nitrobutane. These solvents also dissolvethe cyanogen bromide so that a homogeneous intimate contact may beobtained between the cyanogen bromide and the catalyst. A furtheradvantage of the solution catalyst is that the reaction product cyanuricYhalide is practically insoluble in the Therefore the cyanuric halidesmay be precipitated in the catalyst solution and readily separatedtherefrom Vby ltration. rlurthermore the reaction may be efficientlycarried .out at atmospheric pressure.

Referring to the drawing the cyanogen bromide .is"transferred from thechamber 2u through a line 22V,V which may be a conveyor or a pneumatictube,

into a solution tank 2d where the cyanogen brolmide is dissolved in anitroparafn, such as nitromethane, introduced through a valved line 26./The catalyst (aluminum chloride) is introduced finto a solution tank 28through a line 36 and brought `into solution in nitromethane introducedthrough a valved line 32. The aluminum chloride solution is introducedinto a catalyst converter 34 and into this solution is introduced thesolution .of cyanogen bromide from the solution tank 24. This processcauses an evolution of heat sc that cooling must be provided in a jacket3.6 to maintain the temperature below 60 C.

'Preferably the temperature is maintained at (about 507 C. for one hourtoV complete the reaction. ,After thereaction has been completed cy-;janu'ric halide remains in suspension in the solu-g ftion andV thissuspension may be withdrawn through a line 38 and forced by means of apump l4l'l;through a line 42 into Aa filter pressllli. After theprecipitated cyanuric halide and its mother solution have been forcedinto the filter press 44 more nitromethane is introduced through a line46 to wash mother liquor fromvthe crystalline cyaii'ric halide. Thecyanuric halide then may be forcedinto receiver 48. The mother solutionmay 'then be recycled' in the process.

"Referring now to the production of cyanogen bromide, it has been foundthat the hydrocyanic acid may be reacted with elemental bromine in "thefollowing proportions: f One mol of bromineV (160 grams) is mixed with*an'appropriate quantity of water and to the mixlture is added 1.1 moisof hydroeyanic acid (3U grams). It has been found that different quan--t-lties 'of water may be used for carrying on the consider aso-calledpercentage 'equivalent conweight af HCN chargedV Weight of charged HCNplus total Weight of water It has beenfound that the equivalentconcentration of HCN` charged has a very definite bearing Percent equalsVupon the efficiency of the conversion and the amount of recovery ofcyanogen bromide. For example from 5% to 15% equivalent concentration ofHCN gave the most eiiicient recovery. Any attempts to use higher than a15% equivalent concentration of HCN have been found to y cut down theefficiency of conversion and the amount of cyanogen bromide recovered.

With a 5% equivalent concentration of HCN charged the percentage ofcyanogen bromide collected was approximately With 10% equivalentconcentration of HCN charged the yield of cyanogenbromide wasapproximately 95%. With 15% equivalent concentration of I-ICN chargedthe yield of cyanogen bromide was approximately 93%. With 5% HCNequivalent concentration 'thegpurity of the cyanogen bromide averagesabout 87 whereas with the 15% charge of HCN the purity of the cyanogenbromide isolated was 93% to 96%. If the product obtained when using a15%' concentration of HCN is distilled in the presence of a dehydratingagent, a product of 98% cyanogen bromide content may be obtained.

'As the percentage concentration of I-ICN was'increased above 15% thepercentage yield of cyanogen' bromide fell'oif rapidly and theproduction of ammonium bromide increased. Furthermore, from 1% to 4% ofcyanogen bromide is recoverable from the distillation residue of thebromination reaction.

As the resuit of a large number of `tests it has been found that when 11parts of cyanogen bromide are polymerized'with 1 part of aluminumchloride about Vv8 parts of cyanuric halide are formed. It has also beenfound that a small amount of hydrochloric acidv may be used as apromoter although the yield of cyanuric halide produced when using thepromoter is no larger than when a promoter is not used. The nitromethanefor dissolving the aluminum chloride and cyanogen bromide is preferablyin the anhydrous state. Approximately 75 ml. of nitromethane are used indissolving iive grams of aluminum chloride. vThese same amounts ofcatalyst and solvent, furthermore, 'will dissolve and form a complexsolution with 55 grams of cyanogen bromide. It has been found that asthe number of parts of aluminum chloride per part of cyanogen bromide isincreased the amount of chlorine in the cyanuric halide increases.. VTheaverage yield when using di-iferent amountsxof aluminum chloride willvary from.65% to 75% but the proportion of l11 parts of cyanogen bromideto 1 part of aluminum chloride appears to give the maximum yield andpurity of cyanuric halide.

The analysis of the cyanuric halide produced by the present inventionshows a formula of In this halide, therefore, we may have compounds inwhich three bromine atoms are included in the cyanuric ring or threechloride atoms may be attached in the cyanuric ring. In addition we'mayhave compounds having two bromine atoms and one chlorine atom `inVthegcyanuric ring; two chlorine atoms and one bromine atom in thecyanuric ring. If the aluminum bromide is used as the catalyst thepolymerization product will be cyanuric tribromide. With the preferredprocess using 11 parts of cyanogen bromide with 1 part of aluminumchloride the cyanuric halide contains approximately 85% bromine atomsand 15% of chlorine atoms attached to the cyanuric ring.

One advantageous feature of the present invention is that the cyanurichalides, such as described above, are practically insoluble in thenitroparafns so that When the polymerization is completed the cyanurichalides are precipitated in the reaction liquid and may be readilyfiltered therefrom and easily washed free of the mother liquor with thenitroparaflins. It has been found, furthermore, that the cyanuric halideas produced by the present process is 98% to 100% pure.

If it is desired to produce cyanogen bromide from sodium cyanide thesame equipment may be employed as when hydrocyanic acid is used. Toproduce cyanogen bromide from sodium cyanide the raw materials may beused in the following proportions:

One mol of bromine is added to 125 ml. of 2N-sulphuric acid solutionwhich is placed within the mixer lll. The bromine mixture is cooled andto it is added 55 grams of sodium cyanide dissolved in 125 ml. of water.The sodium cyanide is placed in the solution tank l0 and slowly addedthrough the dropper I2. The reaction is controlled by the coolingsolution in the jacket of the mixer I4 so that the temperature does notrise about 23 C. In this reaction a clear solution of sodium bromide isformed in which is precipitated white crystalline cyanogen bromide.After the reaction has been completed the cyanogen bromide may bedistilled out of the reaction chamber I4 to recover the crystallinecyanogen bromide in the chamber 20. Using the proportions outlined above96% of the theoretical yield of cyanogen bromide having a purity ofapproximately 95% may be recovered. Furthermore, the reaction proceedssmoothly and safely. Also there is a minimum of hydrolysis of thecyanogen bromide to form ammonium bromide.

The cyanogen bromide which is formed either from hydrocyanic acid orsodium cyanide may be effectively polymerized by the process outlinedabove. The loss of cyanogen bromide to ammonium bromide varies directlywith the concentration of the byproduct hydrobromic acid and with theproportions recited in the above examples the loss of cyanogen bromidemay be held at a minimum.

The preferred form of the invention having been thus described what isclaimed as new is:

1. A process of producing cyanuric halide comprising: thoroughly mixinga nitroparafiin solution of a metal halide with cyanogen bromide whilepreventing the temperature from rising above 60 C. until the exothermicreaction is completed to obtain a yield of cyanuric halide above 60% oftheoretical and separating the precipitated cyanuric halide from thereaction products.

2. The process described in claim 1 which is carried out at atmosphericpressure.

3. A process of polymerizing cyanogen bromide to form a cyanuric mixedhalide comprising contacting the cyanogen bromide with a nitroparafiinsolution of aluminum chloride at a temperature of 40 to 60 C. topolymerize the cyanogen bromide and combine chlorine of the catalyst inthe cyanuric ring to obtain a yield of cyanuric halide above 60% oftheoretical and separating the precipitated cyanurc halide from thereaction products.

4. The process dened in claim 1 in which the cyanuric halide isseparated from the reaction solution by filtration.

5. The process defined in claim 1 in which the catalyst solvent isnitromethane.

6. The process dened in claim 1 in which the catalyst is aluminumchloride and is present in the reaction mixture to the extent of about9% of the cyanogen bromide being polymerized.

7. The process defined in claim 1 in which the catalyst is aluminumbromide.

8. The process defined in claim 1 in which the catalyst solvent is anitrocompound of paraflin hydrocarbons having C1 to C4 carbon atoms tothe molecule.

9. The process dened in claim 4 in which 11 parts of cyanogen bromide ispolymerized with 1 part of aluminum chloride to produce approximately 8parts of cyanuric halide.

RAYMOND H. HARTIGAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 666,135 Goepner Jan. l5, 19011,588,731 Henser June 15, 1926 2,414,655 Metcalfe Jan. 21, 19472,416,656 Thurston Feb. 25, 1947 OTHER REFERENCES J. Am. Chem. Soc.,vol. 41, part 2 (1919) Pp. 1241-1248.

In re Migrldichian, 1942 C. D. 554-556, or 544 O. G. 458-459.

Certificate of Correction Patent No. 2,541,053 February 13, 1951 RAYMONDI-I. HARTIGAN It s'hereby Certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows:

Column 5, ldne 35, for the Word about read abo/ve;

and that the said Letters Patent should be read as corrected above, sothat the same may 4conform to the record of the case in the PatentOflce.

Signed and sealed this 8th day of May, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. A PROCESS OF PRODUCING CYANURIC HALIDE COMPRISING: THOROUGHLY MIXING A NITROPARAFFIN SOLUTION OF A METAL HALIDE WITH CYANOGEN BROMIDE WHILE PREVENTING THE TEMPERATURE FROM RISING ABOVE 60* C. UNTIL THE EXOTHERMIC REACTION IS COMPLETED TO OBTAIN A YIELD OF CYANURIC HALIDE ABOVE 60% OF THEORETICAL AND SEPARATING THE PRECIPITATED CYANURIC HALIDE FROM THE REACTION PRODUCTS. 